domain and nameserver setup questions

New to KH and using plesk. I have a few questions would appreciate help, sorry if its been answered already.

I logged first time into plesk and chose full hostname of 'host.mydomain.com' and shared IP, hope those are ok, I want to ask what the fullhostname ('host') is for and am I going to use it in anywhere like nameserver registration

Also I would like to know how I can setup nameservers not only for the primary but if I add other domains inside plesk (and I guess at the registrar but I will check the registrar, I have two domains one is at godaddy another at dotster) For example registering nameservers for secondary domains requires ns1.secondarrydomain.com, ns2.secondarrydomain.com?